Unloading system for volatile liquids



Dec. 18, 1951 E. D. MATTIX ETAL UNLOADING SYSTEM FOR VOLATILE LIQUIDS[mar Filed Dec. 3, 1949 INVENTOR" Jule Ma lin Patented Dec. 18, 1951UNLOADING SYSTEM FOR VOLATILE ropms Emory D. Mattix and Charles W.Stokes, Lake Charles, La., assignors to Cities Service RefiningCorporation, Lake Charles, La., a corporation.

of Delaware Application December 3,1949, Serial No. 131,016

8 Claims. (01. 10s 37) This invention relates to pumpin systems, andmore particularly to a system for transferring volatile liquids such aspropane and butane from tank'cars to storage.

In transferring volatile liquids such as propane and butanes-from tankcars to bulk storage, one or more cars are usually manifolded to asingle delivery line, and natural gas under pressure is admitted to thecars in order to force the liquid to storage. When a large number ofcars are manifolded to the system, the gas pressure may be insuflicientto force the liquid through at the desired rate, andfor this reason itis desirable to interpose a pump in the line to aid in the delivery ofthe liquid to storage. It is necessary at all times to maintain anadequate head of liquid on the pump inlet to prevent damage 'to theequipment.

Due to variations in pressures in the various cars, and also due tovariations in the opening of the valves of the cars, there is alwaystendency for one of the cars to run dry before the remainder are empty.Gas may then enter the delivery line and pump, lowering the head ofliquid in the pump, and in extreme cases, gas may be forced into thestorage tanks. When this occurs, the entire operation must be shut downin order to bleed the gas from the pump, storage tanks, and deliverylines.

Tank cars designed for transporting propane and butanes are usuallyprovided with excess flow valves in conjunction with their dischargevalves to limit the flow of liquid through the valve to a maximum value.When this maximum flow is exceeded, the valves close, and cannot bereopened until the gas pressure on the interior of the car has beenbalanced with the pressure in the car outlet line. Manual setting of thedischarge valve cannot be accurately judged. For this reason it iscustomary to set the discharge valves so that a gallonage per minutesubstantiallybelow the limit of the excess flow valve iswithdrawn fromthe car. It follows that the time required to unload the car is farlonger than the timewhich would be necessary if liquid were beingwithdrawn at the maximum rate allowed by the excess flow valves.

An undesired closure of an excess fiow valve may also cause otherdifficulties in operation. Thus, if the pump were to continue to pull asmuch liquid as before, it would have a tendency to pull additionalliquid from the other cars mani-.

folded to the system, with consequent overloading and progressiveclosing of the other excess flow valves. This results in a condition inwhich the pressure in the inlet line to the pump drops sharply, withconsequent vaporization of liquid,

and gassing in the pump and inlet lines.

It is an object of this invention to provide an unloading system 'forvclatile liquids operative to bleed automatically excess vapors from thesystem, to maintain withdrawal of liquid-from the cars during moderategassing conditions, and to control automatically the rateof withdrawalof liquid from the cars to avoid closure of the excess flow valves, toinsure the most rapid possible unloading of the cars. VF

Theoperation of our improved unloading system will be described moreparticularly in connection with the accompanying drawing in which Fig. 1is a diagrammatic-showing of an un-.

loading system embodyingour invention, and

Fig. 2 illustrates a detail of a tank car unload ing mechanism.

In the operation of our.

open position by means of spring 8. A gas injection line 9 is providedin order to maintain pressureontheinside of the car during unload-.

in operations. Liquid from the cars is drawn through collecting lines I0and pump inlet line I I 5: peller I! located within the flow passage I5and to a, pump I2, which is preferably of a well type in order to insurethat there is sufiicient head of liquid on the pump mechanism at alltimes. If

the pump will flow from the well through the flow passage I5 and throughpump outlet line I6 to storage. The pump I2 is provided with an imdrivenby shaft l8 which is driven by any suitable source of power, the sourceillustrated in the drawing being a steam turbine I9 having a steam inletline 20 and a steam outlet line 2 I.

The outlet line I6 is provided with a flow controller 25, which may beany standard control but which is preferably of the rotameter typesincethis typeof'control is operative over wider flow ranges than othermeter controls. The flow controller is operative to vary the airpressure in line 28 inres'ponse' to variations in flow in outlet line I6to first control a throttle valve 26 normally biased in closed positionin the outletline lfi, and

also a valve 21 also normally biased in closed position in the steaminlet line 20, air supply besystem a number of tank cars are drawn up ona siding and the eduction lines 5 of the cars are connected to the001,-. lection lines ll] of our system. The cars will nor-1 mally beprovided with hand valves 6, and with. excess flow valves .1 which arenormally biased ining obtained from air supply line 21. Valves 2sand 21are split ranged in such a manner that valve 26 will be fully opened atair pressures in line 28 below that at, which the'valve 21 will begin toopen:

After the desired number of tank cars are connected to the collectionlines I0, natural gas will* be admitted under a pressure ofi1say-6O-rprstair through the pressure line 9 and the hand control valve 6 will beopened to allow passage of, liquid from the tank cars to the-pump;At-the same time the flow controller '25 willibefsetisolas to limit thepassage of liquid through the outlet li'ne IE to an amount slightly lessthan that limited by the total capacity of the excess flow valves ofcars manifolded to the system. Thus ifithel-excess flow valves I are ofa type which will allow passage of say 50.gallons per minute beforeclosing; and therearerfivecars manifoldedzto the system;, the flowcontroller 25 will be '-so=-set' as "to. control the flowof'liquidjthrough outlet line l6 to;a-maximumpfslightly less than 250gallons peryminute,

If "only: one car'isimanifolded to; the system, the'pressure of thenaturalgas; combin'ed'with the vapor pressureof theliquidlintheitankcar, will, except in very cold weather or in the eventoflow-natural gas pressure, probably beisufiicient to force the. amount.limited by the excess flow valve of the car 'to storage without thenecessity of using thepurnp. The flow controller. 25. would besetto'passa given amount'say 49 gallons per minute; through the outletline I61, Under these assumed conditions the flow controller wouldoperate to controlzthe pressure in the air control. li'ne'28 to'openvalve 26 to the degree necessary to pass the desired amount of liquid.Ifithis amount isless than that which the valve.26 canpass when it, isfully opened; the, air. pressure will be so con,- trolled'inline. 28 jas to; open, valve 26' only to the degree necessary.v

If'more cars'are maniiolded to the, system and the pressure withinthetank'cars is insufiicient to;

overcome friction in thesystem and" to force the desired quantity ofliquid" through the line l6 when: the valve 25 is wide-open; itwill beneces-- sary to operate-thepump 'l'zf Inthis' ca'se the flow pressurewould be maintaine'd in the air control line 28 -to: open' the-valved 6"to its 1fullest?extent and-:also to open valve 3 in the stea'm dines 20ito the desired degree: For example,- zthecontrol 'IOl'l" valve 23 maybeso set: that=-at pressures, deter-- mined by the-setting-otthe.flowacontrollert-25,.

below 3 p.ls.r i. in. the. controlline. 28-thelvalver2dwwouldremainclosed at alpressure of. say 9, p.. s ,i.,:.

valve 26 wouldbe fully open;,a'nd at intermediate pressures the valve 26wouldbe open .to a lesser degree depending upon ,the pressure.would'be'so adjusted that at. pressures, in control line 28 below ninepounds'the valve would remain closed; but-at pressures above ninepound-sth'e valvewouldb'egin to open; being fully opened at a pressureofl'pound'ss' The 'pounds'pressureinline 28would 'normally be found onlywhen the maximum number of tanki carsztare manifold; ed tothe system;however, in very-cold weather; orin" casepf avfailu'reeof pressuresin-1* the natural gasxinput-to 'th'e cars-itis possible thatthe valve21 would beropened to its fullest degreeewhenless; than: the 1*:maximumnumber- 'of; cars: are: mani-' fflldeldu Thus by means of.thesecontrols. it-is, possibletoaccurately limit-,the withdrawal offluids fromthe otankocarsz to i the amount fixed bvlthe maXie mumcapacity of the excess flow valves of the tank cars, avoiding anyclosure of the valves during operation, and yet allowing the maximumgallonage to be pulled from the tankcars, insuring a rapid andevenunloading'thereof.

The controls described above are suflicient to attain the objects of ourinvention under normal conditions, while'there still remains liquid tobe withdrawn in all of the tank cars. In the event that for one reasonor another one of the tank cars, should run dry before the others,natural gaspwill beforced into the system and will accumulate in: thewelliof the pump I2. In order to insure a continuous evacuation of thisgas from the 'float chamberfuntil the hand valve 6 of the drycar-hasbeen closed to cut off flow of gas into the system, another setofcontrols is provided. Thus the pump l2 has attached theretdfloat chamber32 connected by upper and lower connection lines 33 and 34. The floatchambercontains a float 35, connected with valve control means 36responsive to changes in th'e'liquid level T in the float chamber, andoperative to control the air-pressure in air control line 43 tooperate'a' valve 31 normally biased in closed position in a flaregasline '38 leading from the float chamber 1 32, and a valve 48' normallybiased in open posithe dotted lines in the pump well, the valve con.-

trol means 36 will first operate to open flareg'as valve 31'to evacuatethe gas'accumulation to'a degree which will maintain the liquid levelin'the pump I2 at the indicated height, to permit con.-

tinuous pumping fromthe cars which are not yet empty. If theflow oi gas.into the pump isgreater than the flow which can be. handled by the,flare gas line, valve 31, the. liquidleveli in the float chamber willcontinue to drop. In this, event, the A. valve control, means.36,willoperatetoincrease.

theair pressure in the control lines 39 andtcause the valve 40 tothrottle the turbine l9 .so-that the rate of pumping will be lowered. 1

Thus. under normal circumstances valve. 3?

might beso setas to remain closed at air. pressures in control line 39until atnine poundspressure it isopened. to its fullest extent. Atpressures above nine pounds valve 49 will begin to close, throt tlingcompletely at fifteen poundspressure. Thus by the operation of thecontrols it ispossible to insurethat the pump. is neverinooperationwhen-l there isan inadequatesupply of liquid withinthe pumpwell.

Aspointed out above vaporization in the system may be due to othercauses than one .tank car running .dry beforethe others are empty.vThusa.

closure of c, an excess iflow valve. due to impropen.

maintenance or other abnormal condition-might cause liquid to.bewithdrawn from, the other tank.

cars at such a rate that there is a progressive closing of other excessflow valves and the pull; of the pump will cause the pressure in. theintake line ,H and in the pump well to drop'to. such In;

anextent that vaporization will, take place; such a case the liquidlevel controller 36 will operate valve 3'5 and valve 40 to vent gasesfrom the system and to close down the pump,

It is of note that neither control, alone, is operative to correctconditions which may-"arise within the system givingcause tovaporization in i a manner to assure a minimum unloading time. However,together the controls-operate to main tain a steady flow of liquidthrough the pump until all cars have been evacuated.

Our invention provides an automatic remedy for a vexatious problem inthe art of handling liquefied petroleum gases. It may be easilyinstalled in any presently existing pumping system, and is quicklyresponsive to any changes in the conditions prevailing in the system.

Having now disclosed our invention, what is claimed as new and usefulis:

1. A pumping system for transferring volatile liquids including incombination a pump, pump inlet and outlet lines, a float chamberconnected to the pump, means for varying the output of the pump, a flaregas line leading from the float chamber, a valve in the flare gas line,and a liquid level controller responsive to variations in the liquidlevel in the float chamber, and operative to control the means forvarying the output of the pump and the opening of flare gas line valveto maintain the liquid level in the float chamber at a constant value.

2. A pumping system for transferring volatile liquids including incombination a pump, pump inlet and outlet lines, a float chamberconnected to the pump, means for varying the output of the pump, a flaregas line leading from the float chamber, a valve in the flare gas line,and a liquid level controller operative, in the event of excess gasaccumulation in the float chamber, to control the means for varying theoutput of the pump and the opening of the flare gas line valve in amanner to first vary the opening of the flare gas line valve to ventexcess gas, while maintaining the pump output at a constant rate, andsecond, in the event of excess gas accumulation in the float chamber ata rate greater than can be vented through the flare gas line to lessenthe output of the pump.

3. A pumping system for transferring volatile liquids including incombination a pump, a pump inlet line and outlet line, flow controlmeans in the outlet line, a second means for varying the output from thepump, a flow controller responsive to variations in flow through theoutlet line operative to control both the flow control means in theoutlet line and the second means for limiting the output of the pump tomaintain a constant flow of liquid through the outlet line when thesystem is operating under nongassing conditions, a float chamberconnected to the pump, a third means for varying the output of the pump,a flare gas line leading from the float chamber, and a liquid levelcontroller responsive to variations of the liquid level in the floatchamber and operative to control the third means for varying the outputof the pump and the opening of the flare gas line valve to maintain theliquid level in the float chamber at a constant value.

4. The pumping system according to claim 3 in which the liquid levelcontroller is operative, in the event of excess gas accumulation in thefloat chamber, to first vary the opening of the flare gas line valve tovent excess gas, while maintaining the pump output at a constant rate,and second, in the event of excess gas accumulation in the float chamberat a rate greater than can be vented through the flare gas line, tolessen the output of the pump.

5. A pumping system for transferring volatile liquids including incombination a pump, pump inlet line, and pump outlet lines, a floatchamber connected to the pump, a flare gas line leading from the floatchamber, a valve in the flare gas line, means for varying the speed ofthe pump, and a liquid level controller responsive to variations of theliquid level in the float chamber operative to vary the opening of theflare gas line valve and the speed of the pump in response to variationsin the liquid level in the float chamber whereby to maintain said liquidlevel at a constant value.

6. A pumping system for transferring volatile liquids including incombination a pump, pump inlet line and outlet line, a float chamberconnected to the pump, a flare gas line leading from the float chamber,a valve in the flare gas line, means for varying the speed of the pump,and a liquid level controller responsive to variations of the liquidlevel in the float chamber operative, in the event of a lowering of theliquid level in the float chamber, to first open the flare gas linevalve, and, in the event of a continued lowering of the liquid level inthe float chamber, to reduce the speed of the pump, whereby to cause thesaid liquid level to return to its normal height.

'7. A pumping system for transferring volatile liquids including incombination a pump, means for varying the speed of the pump, pump inletand outlet lines, a valve and a flow meter in the pump outlet line, afloat chamber connected to the pump, a flare gas line connected to thefloat chamber, a valve in the flare gas line, a flow controllersensitive to variations in fiow through the pump outlet line operativeto vary the opening of the outlet line valve and the speed of the pump,and a liquid level controller responsive to variations of the liquidlevel in the float chamber operative to vary the opening of the flaregas line valve and the speed of the pump in response to variations inthe liquid level in the float chamber due to gassing conditions in thepump, whereby to cause the said liquid level to return to its normalheight.

8. A pumping system for transferring volatile liquids including incombination a pump, means for varying the speed of the pump, pump inletand outlet lines, a valve and a flow meter in the outlet line, a floatchamber connected to the pump, a flare gas line connected to the floatchamber, a valve in the flare gas line, a flow controller sensitive tovariations in flow through the pump outlet line operative to vary theopening of the outlet line valve and the speed of the pump to maintain aconstant flow of liquid through the outlet line under nongassingconditions, and a liquid level controller responsive to variations ofthe liquid level in the float chamber operative, in the event of alowering of the liquid level in the float chamber clue to gassingconditions in the pump, to first open the flare gas line valve and, inthe event of a continued lowering of the liquid level in the floatchamber, to reduce the speed of the pump whereby to cause the saidliquid level to return to its normal height.

EMORY D. MATTIX. CHARLES W. STOKES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 868,464 Mann Oct. 15, 19071,050,745 Moore Jan. 14, 1913 1,210,030 Baumann Dec. 26, 1916 1,279,613Traudt Sept. 24, 1918

